1. Field of the Invention
The present invention pertains generally to internal combustion engines and more particularly to a cast aluminum alloy cylinder having an internal passageway communicating with one of the valve cavities on one side of the piston bore and with an intake bore on the other side of the piston bore.
2. Description of Related Art
One known configuration of an air-cooled single cylinder internal combustion engine involves a so-called side valve arrangement in which the intake and exhaust valves are located side-by-side relatively close to one another to one side of the piston bore. The valves are oriented parallel to the piston bore and the valve heads and valve seats are located near the top of the cylinder at the interface between the cylinder and the cylinder head. A valve cavity below each of the intake and exhaust valves communicates with the piston bore around the respective valve head (when the valve is open) via a connecting passageway in the cylinder head. The valves are lifted and opened in appropriate sequence by a common camshaft located in the crankcase below the valves.
The disposition of the intake and exhaust valves immediately next to one another on the same side of the cylinder causes layout problems with the associated appurtenances such as the carburetor and muffler. Even where there is sufficient space to accommodate the carburetor and muffler adjacent the intake and exhaust valves, it is not desirable that they be located next to one another because the exhaust heat emitted by the muffler is deleterious to the proper operation of the carburetor. Consequently, an external intake tube is sometimes routed from the intake valve cavity around the cylinder to the carburetor located on the opposite side of the cylinder from the muffler. This solution adds to the cost of the engine by requiring the manufacture and connection of a separate component, namely the external tube.
It would be desirable to cast an intake passageway leading from the intake valve around to the opposite side of the engine integrally with the cylinder. Unfortunately, such a passageway is necessarily curved because the route circumscribes the piston bore, which curvature precludes the use of a removable casting core.
One prior known cast passageway provides a split passageway which is partially provided by a portion cast integrally with the cylinder and partially provided by a bolt-on cover outboard of the cylinder which completes the passageway. This prior passageway has the disadvantage of requiring a precision machined interface surface which must be sealed by a gasket to prevent air leaks into the intake passageway which would upset the air/fuel ratio established by the carburetor.
Another possible solution known in general to the casting art involves the use of a temporary, non-reusable casting core which can be destructively removed after casting. Such cores are typically made of salt or other refractory material which resists the heat of the molten metal from which the cylinder is cast, and which can be removed after casting by mechanical disintegration or by dissolving the salt in water. The cost of such casting techniques is relatively high.
The present invention provides an economical solution to the problem of providing an intake passageway cast integrally with the cylinder.